The present invention relates to a hand-held belt sander.
Hand-held belt sanders are known in the art. One of such hand held belt sanders is disclosed in the U.S. Pat. No. 4,694,616. It is provided with a driving roller and two deviating rollers having a substantially corresponding diameter. They guide the sanding belt over a sanding base exchangeably arranged on the device. With this device small surfaces of various profiles can be well treated. However, because of the relatively great diameter of the driving and deviating rollers of the hand-held belt sander and because of the coinciding tangential transmission between the rollers and the sanding base, corners and hollow channels are not sufficiently accessible.
The German patent document DE 02 42 26 708 discloses a stationary belt sanding machine with a sanding belt guided over at least two rollers and having a small sanding base. It is provided for sanding works, in which work pieces are to be treated only directly over the sanding belt surface in the embracing region of the rollers, in particular for the production of concave surfaces.
The German patent document DE 0S 39 19 651 discloses a handheld belt sander which in addition to the conventional substantially identical deviating and driving rollers, has a small additional deviating roller for guiding the sanding band tangentially coincidentally between the deviating roller and the sanding base. With this device, corners and hollow channels are substantially better accessible than with other handheld sanders. Since however its construction is based on the conventional handheld belt sander, its belt centering and belt tensioning can be performed in expensive way because of additional, small deviating roller.
Furthermore, the British patent document GB 962 164 discloses a handheld belt sander with the driving roller provided on its periphery with longitudinal grooves. Therefore an improved for transmission to the sanding band is obtained. The handheld belt sander is however heavy, uncomfortable, and complicated.
In the known handheld belt sanders the belt centering is performed by turning or tilting of the deviating rollers which rotate on roller or metal sliding bearings about a fixed rotary point on the roller axis. The deviating roller is mounted by screwing or safety rings on its axle. An exchange of the deviating roller is complicated. Moreover, in the known belt sanding devices the sanding band is tensioned by displacement of an operating lever which is operative for actuating the deviating rollers at the outer side of the sanding belt. However, the operating lever is difficult to axis and not easy to operate.
In belt sanders, independently from their size of the width of the belt, the sanding belt is driven through a rotatable driving roller by a frictional connection. Therefore, the force transmitted to the belt is dependent on the friction value between the inner side of the belt and the roller, as well as on the normal force of the belt on the roller, and on the embracing angle. However, in the known belt sanders these values are not sufficient.